(i) Technical Field
The present invention relates to a method of fabricating a semiconductor device.
(ii) Related Art
An FET (Field Effect Transistor) such as a HEMT (High Electron Mobility Transistor) using a nitride semiconductor has attracted attentions as an amplifier that operates at high frequency and high output such as an amplifier for a portable telephone base station. An Al (aluminum) film has been used for an ohmic electrode of the FET using the nitride semiconductor as disclosed in Japanese Patent Application Publication No. 10-223901.
However, a hillock is formed in the Al film of the ohmic electrode because of heat treatment. When the hillock comes close to or makes contact with a metal layer other than the ohmic electrode, the pressure resistance decreases or the reliability decreases.